As Internet technology develops, Internet becomes more and more complex, and the traffic over Internet grows in an explosive manner. Because the Internet Protocol (IP) technique employs an Open Shortest Path First (OSPF) routing algorithm, each data stream is routed to the destination in the shortest path, which inevitably causes uneven traffic distribution among the paths. For example, some paths are congested with heavy traffic, while the others are in idle state and are not utilized effectively. As shown in FIG. 1, the path between node 1 and node 2 is congested with heavy traffic.
For the purpose of solving the problem of congestion resulting from uneven traffic distribution, a Traffic Engineering (TE) method is put forward, i.e. some traffic is led to relatively idle paths by force, so as to balance the traffic and alleviate congestion. As shown in FIG. 2, the traffic that was planned to be routed from node 1 via node 2 to node 4 is led to the path from node 1 via node 3 and node 2 to node 4.
Multi-Protocol Label Switch (MPLS) is a label switching technique, which can establish a Label Switch Path (LSP) in the IP network in advance, and when traffic comes into the network, switch the traffic along the LSP to the outlet. MPLS technique can import different traffic streams to different LSPs for switching.
MPLS TE is the best technique for implementing traffic engineering over the IP network; MPLS TE diverts the network traffic to idle paths by means of the LSPs established in advance with MPLS technique, thereby attaining the objective of traffic engineering.
At present, in the IP network, the procedures for implementing traffic engineering mainly include:
1. Collect the traffic engineering (TE) information of the IP network. The TE information is used to calculate TE paths. In MPLS TE technique, topology discovery is usually implemented by routing protocol extensions, such as Open Shortest Path First (OSPF) protocol, or Intermediate-System to Intermediate-System, ISIS) protocol. Those routing protocols can be used to collect network topology and relevant TE parameters.
2. Calculate TE routing according to the collected network TE information, with the current situation of network traffic as the constraint. In simple terms, it means to calculate how to route the traffic streams through appropriate paths without causing congestion in accordance with the current situation of the traffic. In MPLS TE technique, the commonly used constraint-based route calculation algorithm is Constraint-Based Shortest Path First (CSPF). To calculate the constraint-based routing, each device in the network should run the CSPF algorithm.
3. Deploy the calculated constraint-based paths into the network. In MPLS TE technique, constraint-based paths are referred to as Constraint-Route Based Label Switch Paths (CR-LSPs), which are usually deployed into the network with an MPLS TE messaging protocol. For example, the MPLS TE messaging protocol can be Resource reSerVation Protocol-Traffic Engineering (RSVP-TE).
4. Forward the traffic according to the deployed paths.
As Internet develops further, the access network part of some L2 networks (e.g. metropolitan area network (MAN)) becomes more and more complex, and the problem of uneven traffic distribution and congestion has occurred in such L2 networks. Therefore, it is an increasingly urgent task to deploy traffic engineering over L2 networks.
Presently, the method for deploying traffic engineering to L2 network is: migrate the MPLS TE applicable to IP network directly to L2 network.
However, because MPLS TE is implemented based on IP network, a prerequisite for normal operation of MPLS TE is: the entire network is accessible on the IP layer. Therefore, for the purpose of migrating MPLS TE technique into a L2 network, each device in the L2 network should be configured with the IP address and run IP protocol and IP routing protocol. What is more important, the CSPF algorithm, OSPF/ISIS routing protocol, and RSVP-TE protocol, etc., which consume software and hardware resources severely, must be run on each device in the L2 network. L2 devices are relatively simple devices by nature and only L2 switching function is required on these devices, and therefore, the costs of L2 devices can be very low. However, if IP protocol, OSPF/ISIS algorithm, CSPF algorithm, and RSVP-TE protocol are implemented over L2 devices, the complexity in software and hardware increases severely, and the equipment costs increase heavily. Furthermore, because each L2 device must be configured with an IP address, the consumption of IP address resource increases.
In addition, there is only an L2 network control plane in L2 network originally; however, after MPLS TE is migrated into the L2 network directly, an IP/MPLS control plane is added over the L2 network control plane. As a result, the network architecture and logic is more complex, the network deployment and maintenance work is more complex, and the on-going maintenance costs increase greatly.